Synchronized pulse producer



J. M. DODDS ETAL.

SYNGHRONIZED PULSE PRODUCER May 25, 1948.

. Filed D60 18, 1943 Lu m w .0 M g z C R w T A a n N 0 I. D i... w w 0 3A w m E m 1 lkfi m l .m W in lllll ll ll l 0 Wnwq 3 l A INMF/VTURS.

JOHN MATHIESON DODDS GRAHM JOHN SCOLES MICHAEL EDWARD HAINE ROBERTFENWICK ARCHER By M ATTORNEYS Patented May 25, 1948 SYNCHRONIZED PULSEPRODUCER John Mathieson Dodds, Timperley, Graham John Scoles, EastSheen, London, Michael Edward Haine, Sale, and Robert Fenwick Archer,Man chester, England; assignors to vMetropolitan-- Vickers ElectricalCompany Limited, London, England, a company of Great BritainApplication. December. v18, 1943, Serial No. 5143862 In Great BritainSeptember 20, 1940 Section 1, Public. Law 690, August 8, 1946. Patentexpires September 25,1960

6 Claims.

This invention relates to electrical frequency dividers of thek-indcomprising a grid-controlleddischarge device-or Thyratron- (aregistered trade-mark having an anode load impedance with outputterminals, a time constant cathode circuit of parallel resistance (whichmay be variablelfland capacity of appropriate-values, the grid of saidtube being connected, preferably through a. resistance,- to theendofsaid time con.- stant circuit remote from the cathode, and the aforesaidcombinationbeing-subjected to a supply frequency voltage so that theremay be obtained from said outputterminalspulses having a frequency whichis a sub-multiple of that of the input supply.

Heretofore the voltageoi supply frequency has been applied across-thewhole combination above specified, and with this arrangement the otput,

pulses of sub-multiple frequency are of sinusoidal Wave forminnature, sothat, if sub-multiple fre-.

quency pulses of rectangular wave form were required, the output pulseswould be passed over a network f appropriate and per se known form.

The object of the present invention-is to provide simple and efiectivemeans-for deriving-low power outputs-of substantiallyrectangular waveform and at accurate sub-multiples of supply frequencies;

According to the present invention pulses of rectangular type and ofsupply frequency are applied to the Thyratron by'mea nsof a hard valvehaving its anode connected to the time constanteircuit and having thesinusoidal supply voltage appliedbetween the grid and cathode, thesupply voltage being sufliciently high to cause this hard valve tosaturate rapidly, whilst direct current --an'ode suppilyis preferablyused for the "Thy-ratron.

It has been found advantageous in some cases to divide'the resistance ofthe time constant circuit into two portions one of which isconveniently-variable whilst the junction point of these resistances isconnected through an appropriate relatively high resistance to thepositive supply'of the Thyratron whereby a backing-off current-is passedat every half-cycle, thus preventing the discharge of the time constantcircuit condenser until the cathode potential attains the requiredvalue. By this feature the' peratlon of the f-r-equency divider proceedssharply and with certaint from onesub-multiple .of the supplyfrequency'itothenext. 1

According to a subsidiary ,feature of the inventlon the frequency=i'livider is provided with a-n 0111 put 'irequencymeter. inthe rormlof1a milliammeter or the like. connected to the output terminals of thefrequencydivider in association with a rectifier system.

To enable the-invention to be clearly understood it will now bedescribed with reference to the accompanying drawings, in which:

Fig. 1 is an electrical diagram illustrating the simplest form. offrequency divider in accordance with the invention and including also .asimple arrangement of output frequency. meter.

Figs. 2 .to 7 inclusive are graphs illustrating the operation of thearrangements illustrated in Figs. 1 andii, and v i Fig. 8 is anelectrical diagram illustrating the.

referred arrangement in accordance with the invention, includingthepreferred output frequency meter system. 7

Referring first to .Fig. 1 of the accompanying drawings, at 'T is shownthe Thyratron having thean'ode load resistance R, the time constantcathode circuit comprising the condenser Cl and resistance RI, thelatter being preferably variable, and the grid currentlimitingresistance R2. If the iThyratron 'Iis a "Mazda? T.3 1 Mazdabeing a registered trade-mark) suitable values for C l, and RI are 4microfarads and-10,000 ohms respectively whilst the resistance R2 may be500,000 ohms.

The "Thyratron T is controlled by a supply frequency sine wave voltagewhich is applied to a hard-triode ,AQ/HL, the grid of which has thesinusoidal supply voltage applied to it, the Thyratron receiving itsoperatingpower from the direct current source. As shown the hard triodeAC/I-IL has its anode connected to the time constant circuit CLLRI andhas the supply volt,- age applied to its grid, preferably through aresistance R3 which may be of.5,00 0,000 ohms. This hard valve maybe aMazda valve type AC/HL and the supply voltage may be volts, so thatduring every positive half-cycle the hard valve will be caused tosaturate rapidly, thus impressing voltages of sufficiently rectangulartype form upon this Thyrat'ron combination to cause it to generatesubstantially rectangular pulses of sub-multiple frequency.

Referring to Figs. '2, '3 and 4, it may be assumed that the circuitshown in Fig. 1 has its parameters chosen for any particular value of"the division factor n; then the hard valve AC/HL only 00 ducts when theThyratron conducts, although it becomes conducting for a period ofhalf-acycle during each cycle. The application of the 110 voltsalternatingsupply to the grid of the hard valve through the resistanceR3 ensuresithat when the hard valve does conduct it saturates rapidly,thus ensuring the application of a substantially square voltage waveform to the Thyratron which in turn produces a substantially square waveform output across the load resistance R.

If the Thyratron T.31 does not conduct the wave forms at various pointsare as shown in Fig. 2 wherein the sinusoidal wave is that applied tothe grid of the hard valve AC/HL, the cathode potential CAC/HL of whichis the hor'- zontal base line. The anode supply voltage on the"'I'hyratron is assumed to be 300 volts direct current and the periodicgrid potential of the Thyratron is represented by the three lines G'I3I.Thus, under these conditions the voltages applied to the Thyratron areas shown in Fig. 3 wherein TA is the anode voltage, TC the cathodevoltage and TG the grid voltage of the 'I'hyratron during eachinadequate positive half-cycle of the voltage applied to the grid of thehard valve AC/HL. There is a critical Thyratron cathode potential TC(Fig, 3) such that if the cathode potential is higher than this the gridbiasing of the Thyratron is too high for the Thyratron to fire.

Assume now that the circuit of Fig. 1 is set to operate with 12:1, thenduring each cycle of the supply frequency the Thyratron conducts for aperiod of /100 second and its anode potential falls. During eachconduction period of the Thyratron the condenser C I becomes chargedcausing the Thyratron cathode to become positive with respect totheThyratron grid. During each non-conducting half-cycle of theThyratron the condenser CI discharges through the resistance RI and theThyratron cathode potential falls to such a value during the half cyclethat the Thyratron is not too strongly biased to fire on the nexthalf-cycle. These conditions are shown by Fig. 4 wherein TA representsthe Thyratron anode voltage, 'IG the 'I'hyratron grid voltage, CCP thecritical cathode potential of the Thyratro'n and TC the pulsatingpotential of the Thyratron cathode.

If now the value of the time constant resistance RI is increased thedischarge rate of the condenser C I is reduced until at the beginning ofthe next half-cycle the bias of the Thyratron is too great for firing,so that for the purpose of illustration it may be assumed that 11:2, asindicated by Fig. 5. By further increasing R, a succession of values 2,3, 4, 5 for 12 may be obtained.

It was found under certain circumstances in practice that conditionsindicated by Fig. 6 were sometimes obtained, that is, the operation ofthe circuit during increase of resistance RI did not proceed sharplyfrom one sub-multiple of frequency to the next. To avoid thispossibility it was arranged that if the "Thyratron did not fireimmediately at the beginning of the halfcycle of positive voltage on thegrid of the hard valve, the Thyratron would be prevented from firing atall during that half-cycle, and this was achieved by dividing theresistance RI into two portions, RI and R4, as shown in Fig. 8, andconnecting the junction point of the resistance parts RI and R4 to thepositive supply to the Thyratron. In this way a backing-H current wascaused to flow at every such half-cycle in question, to prevent thedischarge of the time constant condenser CI. This current is that of thecircuit of the resistances R and R4 and thence through the hard valve.The resultant appreciated that this modification may in some casesprevent operation of the circuit for values of 11:1 and possibly 2,necessitating reduction of the capacity of the time constant condenserCl such as from 4 to 2 microfarads, thus reducing the voltage developedacross it and requiring a reduction in the value of the resistance R4 inorder to prevent the voltage developed across this resistance by thebacking-off current from becoming so small as not to prevent thedischarge of the condenser C! during those conducting half-cycles of thehard valve for which the 'Ihyratron was non-conducting. It was foundthat with CI=2 microfarads, R4=3,000 ohms and R5=50,000 ohms, thecircuit covered the frequency division range of n==1 to 14.

The simple output frequency meter shown in Fig. 1 may be a smallmilliammeter M supplied from the output leads through a condenser C2 andrectifier or rectifier system UI so that the meter measures therectified current. The meter may be calibrated and its scale chosen togive readings of full supply frequency and sub-multiples thereof. Therectifier U2 is added to render the law of the meter scale more nearlylinear by by-pass'ing current as the voltage across a smoothingcondenser C3 increases with the higher frequencies of operation.

In Fig. 8 is also shown the preferred form of frequency meter comprisingthe milliammeter M supplied from the output circuit of the Thyratronwith unidirectional current through the condenser C2, resistance R1 andrectifier bridge UI with smoothing condenser C3, smoothing. choke L,resistance RS and bridging rectifier U2, the latter being provided torender the law of the scale of the meter M more nearly linear bybypassing current as the voltage across the condenser C3 increases withthe higher frequencies of operation. The resistance It! serves to limitvthe current through the rectifiers on the initial charging of thecondenser C2 when the high tension supply is switched on.

In the final arrangement adopted as the result. of experiments the MazdaThyratron T3]. was replaced by a Mazda Thyratron type T41 and the hardvalve Mazda AC/HL was replaced by a Mazda type P.41.

We claim:

1. An electrical frequency divider, comprising a thermionic dischargedevice having an anode provided with a load impedance and outputterminals, a cathode having a time constant circuit connected thereto,and a controlling grid connected to said circuit remote from thecathode, a source of sinusoidal supply frequency, and means connected toreceive said sinusoidal supply frequency and connected to said timeconstant circuit for subjecting said discharge device to voltages ofsaid supply frequency and of substantially rectangular form wherebysubstantially rectangular pulses of sub-multiple frequency aregenerated.

2. An electrical frequency divider, comprising a thermionic dischargedevice having an anode provided with a load impedance and outputterminals, a cathode having a time constant circuit connected thereto,and a controlling grid connected to said circuit remote from thecathode, a source of sinusoidal supply frequency, and a valve having acathode and grid connected to said sinusoidal supply frequency, and ananode connected to said time constant circuit.

3. electrical frequency divider according to claim 2, wherein said valveis a hard valve, and the anode thereof is connected to said timeconstant circuit at a. point remote from its connection to the cathodeof said discharge device.

4. An electrical frequency divider according to claim 2, including asource of direct current for exciting the anode of said thermionicdischarge device.

5. An electrical frequency divider according to claim 2, wherein saidtime constant circuit comprises resistance and capacity in parallel.

6. An electrical frequency divider according to claim 2, including meansfor connecting the positive side of a source of direct current supply tothe anode of said thermionic discharge device, and wherein said timeconstant circuit comprises resistance and capacity in parallel, saidresistance being divided into two portions and having the junction pointof said portions connected to said positive supply for said thermionicdischarge 20 device.

JOHN MATHIESON DODDS. GRAHAM JOHN SCOLES. MICHAEL EDWARD HAINE. ROBERTFENWICK ARCHER.

6 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,927,425 Mark Sept. 19, 19332,036,495 Pohontsch Apr. '7, 1936 2,100,700 Schlesinger Nov. 30, 19372,102,951 Hackenberg Dec. 21, 1937 2,106,713 Bowen Feb. 1, 19382,185,635 Keck Jan. 2, 1940 2,282,130 Hadfield May 5, 1942 FOREIGNPATENTS Number Country Date 450,986 Great Britain Jan. '7, 1936 488,842Great Britain July 14, 1938 OTHER REFERENCES Publication RCA 885 GasTriode, 4 pages, RCA Radiotron Co. Inc., 1934. (Copy in Division 51.)

